1. Field of the Invention
The present invention relates to a gate turn-off thyristor or similar pressure-contact type semiconductor element, and to a power converter which utilizes the pressure-contact type semiconductor element.
2. Description of the Related Art
Pressure-contact type semiconductor elements such as gate turn-off thyristors (GTOs) are widely used in fields such as electric power and industry. Particularly the pressure-contact type semiconductor elements which are designed for high-power use demand ever greater capacity to meet the exigencies of high withstand voltage and heavy current. For this purpose it is vital to increase the number of element unit (the number of segments), and semiconductor substrates are becoming larger and larger.
FIG. 1 is a cross-sectional drawing of a conventional GTO. In FIG. 1, a pressure-contact type semiconductor element 1 comprises a semiconductor substrate 2, a gate electrode 2a formed on the front surface of the semiconductor substrate 2, a cathode 2b formed on the front surface of the semiconductor substrate 2, an anode 2c formed on the rear surface of the semiconductor substrate 2, a cathode-side buffer plate 3a, an anode-side buffer plate 3b, a cathode post electrode 4, an anode post electrode 5, an end passive component 6, a circular gate conductor 7 adjoining the gate electrode 2a, a gate lead 10 connected to the circular gate conductor 7, a gate lead 24 on the cathode side, a hold 22 which presses the circular gate conductor 7 elastically against the gate electrode 2a, and a circular insulating housing 11 which houses the semiconductor substrate 2, cathode post electrode 4, anode post electrode 5 and circular gate conductor 7.
When a gate current is applied to the gate lead 10, it flows by way of the circular gate conductor 7 to the gate electrode 2a, and the semiconductor element turns on.
In a semiconductor element configured in this manner, while segments in the vicinity of the gate lead are easily switched, those on the opposite side to the gate lead are not.
As semiconductor substrates become larger, increased imbalance of gate current distribution on the surface of the semiconductor element leads to a requirement for redundancy in the current withstand of the element, and current density falls.